In the field of graphic arts, in order to improve the regeneration of continuous gradation images with halftone dot images or the generation of line images, image formation systems exhibiting ultrahigh-contrast (particularly, .gamma. is 10 or more) photographic characteristics are necessary.
As methods for obtaining high-contrast photographic characteristics, lithographic development systems utilizing the so-called "infectious development effect" have been used for long. However, they have the problem that the developing solutions are unstable and hard to use.
On the other hand, as methods for obtaining high-contrast images using more stable developing solutions, there are methods described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,221,857, 4,332,878, 4,634,661, 4,618,574, 4,269,922, 5,650,746 and 4,681,836.
These image formation systems are systems for processing hydrazine derivative-containing silver halide photographic materials of the surface latent image type with stable MQ developing solutions (in which hydroquinone is used in combination with a p-aminophenol) or PQ developing solutions (in which hydroquinone is used in combination with a 1-phenyl-3-pyrazolidone) having a pH of 11.0 to 12.3 to obtain ultrahigh-contrast negative images in which .gamma. exceeds 10. According to these methods, ultrahigh-contrast and high-speed photographic characteristics can be obtained, and sulfites can be added in high concentration to the developing solutions. Therefore, the stability against air oxidation of the developing solutions is remarkably improved, compared with the conventional lithographic developing solutions.
Also for photographic materials for illuminated rooms used in page making-up and dot to dot work steps, when overlay contact of halftone dot originals, and line originals is tried faithfully to the originals, methods for forming ultrahigh-contrast images are required. Also for this purpose, the above-mentioned image formation systems using hydrazine derivatives are effective, and specific applications thereof are disclosed in JP-A-62-640 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-62-235938, JP-A-62-235939, JP-A-63-104046, JP-A-63-103235, JP-A-63-296031, JP-A-63-314541 and JP-A-64-13545.
In U.S. Pat. Nos. 4,998,604 and 4,994,365, hydrazine compounds having repeating units of ethylene oxide and hydrazine compounds having pyridinium groups are disclosed. However, as apparent in these example, the high contrast is insufficient, and it is difficult to obtain sufficiently high contrast and necessary Dmax under practical developing conditions.
On the other hand, it is known that enediols such as ascorbic acid function as developing agents, and attention is given to them as developing agents having no ecological and toxicological problems. For example, in U.S. Pat. Nos. 2,688,549 and 3,826,654, it is described that image formation is possible under high alkaline conditions of pH 12 or higher. However, high-contrast images can not be obtained by these image formation methods.
Some attempts have been made to increase the contrast in development systems using ascorbic acid. For example, Zwicky describes that the use of ascorbic acid as a sole developing agent causes a kind of lithographic effect to appears (J. Phot. Sci., 27, 185 (1979)). However, this system was considerably low in the contrast, compared with hydroquinone development systems. Further, JP-B-49-46939 (the term "JP-B" as used herein means an "examined Japanese patent publication") discloses a system in which ascorbic acid is used in combination with a bis-quaternary ammonium salt. This system has the development accelerating effect, but scarcely shows the contrast increasing effect. JP-A-3-249756 and JP-A-4-32838 also describe the effect of using ascorbic acid in combination with a quaternary salt. However, the contrast of images obtained is not sufficient. Furthermore, JP-A-5-88306 describes that high contrast is obtained by using ascorbic acid as a sole developing agent and keeping the pH at 12.0 or higher. However, this system also has a problem with respect to the stability of a developing solution because of its high pH.
There is an example in which a particular developing solution containing ascorbic acid and a hydrazine derivative as main components is used to obtain a development system high in sensitivity and low in stain and fog (U.S. Pat. No. 3,730,727). However, no reference is made to contrast enhancement.
It is known that photographic materials containing hydrazine are processed with ascorbic acid developing solutions, and disclosed in U.S. Pat. No. 5,236,816 and WO 93/11456. However, both are insufficient in terms of the contrast. In the latter, the contrast is enhanced by adding an amine to a developing solution, but this is environmentally unfavorable. A development processing method has therefore been desired in which toxicologically preferable ascorbic acid is used as a developing agent to obtain a high-contrast image.
In the usual PQ or MQ development, contamination with silver sludge in the developing solutions often causes a problem, and this problem has been desired to be solved.
The system for forming ultrahigh-contrast images using hydrazine derivatives is a system using a dihydroxybenzene compound such as hydroquinone as a developing agent, as described above, and have some disadvantages from the ecological and toxicological viewpoints.